This invention relates to registration of stock such as sheet or web stock, for accurately performing an operation such as stencilling thereon. The invention was developed chiefly for the field of stencilling and will therefore be explained largely in that background, although having other potential applications.
The well known art of screen stencilling is widely employed for depositing coating materials for various decorative and for functional purposes. Such coating materials include substances such as inks, adhesives, and/or a variety of other functional and/or decorative substances. They are applied to web or sheet substrate stock of paper, polymeric materials, wood or cloth and laminates of various materials. The resulting products include posters, prints, decalcomania, graphic designs and others too numerous to list.
To accurately deposit the coating substance, position registry of the substrate stock must be accurate. Although the degree of accuracy required will vary depending upon the operation and the product involved, the stencil printing of multiple color inks requires a high degree of registration accuracy during the successive printing steps of individual colors. Unfortunately, such accuracy is not always obtainable using known techniques. For example, a common registration technique for web stock involves a punched hole through which a correspondingly shaped pin is projected at each printing station. The edges of the hole often become progressively more and more distorted at each station into an elongated configuration, preventing accurate registration. Also, the holes render areas of the stock otherwise useless and unsightly. Further, the stock must be penetrated for each registry by an inserted pin, so that the rate of stock movement is limited to allow this insertion and withdrawal.
The application of special registration tabs as set forth in U.S. Pat. No. 3,783,059 is often advantageous. But tabbing of the stock is not always possible or desirable either.
As to sheet stock, attempts to use the leading stock edge for registration are often not practical, particularly for accurate registry, since this edge is the one placed in the clamps as on the impression cylinder of a press. The registration equipment for this is disadvantageously within the range of the stencil screen and squeegee. Hence, the leading edge of the sheet is thus in a crowded area, affording only limited clearance. And, when lightweight or soft sheet stock is encountered, the conventional cylinder guides that must push the sheet back by engaging the front edge of register it, frequently cannot effectively push such stock without at least wrinkling the sheet, rendering the registration unreliable.